Modified weak-acid isopropanol process



E. H. AMlcK, JR MODIFIED wEAK-ACID IsoPRoPANoL PRocEss Sept. 2, 1952 5 Sheets-Sheet l- Filed April 5, 1950 3 Sheets-Sheet 2 E. H. AMICK, JR

MODIFIED WEAK-ACID ISOPROPANOL PROCESS Sept. 2, 1952 Filed April 5, 1950 OOG OO OOM OOM O .v 6/ n x W NRNMl/f ON \\Od0o&/ 2 a A\\\ T d M O W m T o w OG J )n m T O@ a o D w OOM. C

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JOIOU E. H. AMlcK, .JR MobIFIEn wEAx,.,Ac1 D IsQPRoPANoL. PRocEss OO..u

Sept. 2, 1952 Filed April 5, ,195o

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Patented Sept. 2, 1952 MDIFIED WEAK-ACID ISOPROPANOL PROCESS Erwin H. Amiek, Jr., Linden, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application April 5, 1950, Serial No. 154,127V

15 Claims. l

This invention relates to a process for producing isopropanol by the indirect hydration of propylene. More specifically the invention relates to a modiiied Weak-acid isopropanol process.

The weak-acid isopropanol process comprises the following essential phases:

1. Absorption of propylene in approximately 70% sulfuric acid at about 170 F. and approximately 250 lbs. per sq. in. gauge pressure to form a mixture which probably consists of isopropyl sulfates, isopropyl alcohol, isopropyl ether, and traces of polymer. The concentration of propylene in the feed stream is a factor which is correlated with the pressure employed in the absorber; for example, with concentrated propylene (75-85 mol percent) a simplified absorber design is used and absorption can be carried out at comparatively low pressure, for example, 200-250 p. s. i. g. On the other hand, a more dilute propylene feed (50-55 mol percent) requires a higher absorber pressure and possibly the use of an absorption system with several contact stages for high propylene recovery.

2. Additional hydrolysis by dilution of the extract leaving the absorber to approximately 45% sulfuric acid (on the hydrocarbon free basis) and maintaining the extract at about 190 F. for a period of about minutes residence time.

3. Distillation of the hydrolysis products (alcohol and ether) from the spent acid in a generator-stripping zone and reconcentration of the spent acid from about 45% to 70% strength.

In the weak-acid process the generator-stripping zone is operated so as to remove as substantially completely as possible all organic material from the hydrolyzed extract. This is accomplished by previously diluting the extract with water from an acid concentration of about 70 weight percent on an organic free basis to about 45 weight percent on the same basis. and supplying suicient heat to the generator-stripping zone to remove substantially all the propylene from the dilute acid in the form of isopropyl alcohol, isopropyl ether and propylene, but particularly in the form of the alcohol. The dilute spent acid is subjected to reconcentration in reboiler equipment such as the well-known Simonsen-Mantius concentrators and the steam generated therein is employed in the generatorstripping zone to eiect the stripping. Reconcentration of the spent acid is a costly procedure and is often hampered by the fact that the concentrators become fouled by the presence therein of sludges and tars resulting fromthe continuous 2 f application of heat upon organic material not completely removed from the acid extract inthe generator-stripping zone.

It is anobject of this invention to produce isopropanol in an indirect hydration process employing Weak sulfuric acid in which reconcentration of the sulfuric acid is avoided.

This and other objects of the'invention are accomplished by forming an acid extract by absorbing propylene or its equivalent, e. g., isopropyl alcohol or isopropyl ether, in sulfuric acid of -70 weight percent, preferably about 65-68 weight percentto a saturation of 0.60- to 1.50, preferably 0.90 to 1.30 moles of propylene per mole of sulfuric acid and thereafter stripping said extract, without dilution with Water, in a generator-stripping zone under pressure below atmospheric pressure, or by stripping with a propylene-containing gas or inert gas such as N2, CO2, etc. at atmospheric or subatmospheric pressure. Instead of removing all organic material as completely as possible from the extract inthe generator-stripping zone, only a small amount, v3-20 Weight percent, preferably about 5-10 Weightpercent, of the propylene is removed from the extract during the stripping in the form of isopropanol, and isopropyl ether and some regenerated propylene in minor amount. Only sufficient Water is added to the partially stripped acid extract, preferably in the form of steam to the generator-strippento replace that water consumed in hydrating the small amount of propylene removed from the generator in the form of isopropanol and isopropyl ether.

`It is necessary to carefully adjust the heat balance of thegenerator so that dilution of the acid doesnot occur. This heat balance can be maintained by (1) regulation of temperature of extract, 2) control of steam temperature and pressure, or (3) use of a hot stripping gas.

Acid extract of reduced saturation, but still containing 60-70 Weight percent sulfuric acid is withdrawn from the base of the generator and returned to the upper section of the absorber for further absorption of. propylene to increase its strength to the original saturation. The cycle is then repeated. Vapors from the stripping zone are processed in the usual way. They are first caustic-scrubbed with dilute aqueous caustic for removal of entrained acid vapors, condensed to knock out the crude isopropanol, and the uncondensed vapors are further water-scrubbed for removal of remaining traces of alcohol therefrom. l

Any propylene or hydrocarbon vapors remain` f0.6 tolle ing uncondensed pass through the water scrubber and are either burned, returned with the feed gas to the absorber, or employed as stripping gas in the recovery of isopropanol from the generator-stripper.

The invention will be more fully understood from the following description of the invention in conjunction with the accompanying Figure l which is a diagrammatic cross-sectional View of typical equipment employed in the process.

Referring to Figure l propylene-rich gas or liquid which is substantially free of C4-unsaturates, particularly butadiene, is introduced through line 2 into absorber l by means of jets to obtain dispersion of the propylene through the reaction mixture. Recycled sulfuric acidpropylene extract of approximately 60-70 Weight percent acid strength previously prepared by absorbingpropylene in 60-70 weight percent sulstripped in generator 6 'is'withdawn'fro'mgenerator 6 via line H and'oontiiiuoiislyihlmped by means of pump l2' through lines 't3 and? intothe absorber at point or 'pluality' of' rpointsl near the top thereof, VThe'ab`s `ir.b"erLis operatedfat a temperature in the'range of Illllnl.' to 190 F. and asuitable pressure in'thejrfnge'of 100 to 500 p. s. vi. g., preferably `abbut1250 p.. s. iig. depending on the concentration'of .propylene in the feed stream. In the absorber 'the' ,projpylene `reacts with the acidinf thepropylne extract tomform a more saturated" extract product containing Yfrom moles of pr'opylehe vper mole of sulfuric acid, preferably about `0.9"t'o' 1;3 moles of propylene' per mo'lefof acid. .'.Inf'no case should the acid strength ofthe;xtractfalllbelow 60% on'a hydrocarbon lfreebasis, nor's'hould it be allowedjto exceed 70% The'xtract product gravitated con- `zu'iou's'hfto the' bottom of' the tower and isremovcdthreiromvialine 5 toi the `alcohol gen- 'era'tort` without-,dilution withfwater, Unadsorbed gases'lean in 'pro'pylene leave the'towervia line 'The absorption'raction'is exothermicjto the extent of -ar'iproXii'nately25,;000 B.-t. u. per mole of propylenefabsorbed, and'this heatis removed, if necessary, by lcooling the 'extract by means of a cooler ifins'ert'e'd 'inline [L Circulation of the extract from the bottom of the absorber through cooling zone thence baci: tothe top of the absorber is avoided.

Heatexchang'erj 35 acts as a heater or cooler dependingfu'pon 'heat losses,v "etc. inthe generator,

and ismplo'y'ed 'to maintainfthe necessary heat balance. The amountof hydrocarbon in the form of pro'pylene orl its hydration products removed from the extract'in the generator -is-purposely limitedso that' a larger quantity of material is Yrecycled f through cooler l 'to bring down the temperature so that the temperature -oi the absorptionis maintained constant.

Theacid extract leavingthe` bottom of tower i via line is a mixture of isopropyl alcohol, isopropyl sulfateisopropyl ether and free sulfuric acid. This extract ispreierably of about 0.9 to 1.3 saturation, i. e. it contains 0.9 to 1.3 moles of propylene per mole Vof sulfuric acid. 'I 'he extract has an acid strength of (iO-70 weight percent on a hydrocarbon free basis, preferably about 'G5-68 Weight percent.

Alcohol generatorts the usual type of stripping column except 'thatin vthis process itis of reduced size due to the nature of the stripping occurring therein. The number of trays or plates is considerably less vthan that required in the conventional process where complete stripping is generator/maybeoperated at a pressure slightly below atmospheric pressure, e. g. 740-750 mm.

"among other factors, of the acid concentration or the extract undergoing stripping but lies generally in the range of 20D-750 m-rn. For example, 'a't'61-5 Weightpercent acid in the extract the Hg. At '70 Weight percent acid lower pressures such as 270-280 mm. Hg are required to minimize propylene regeneration. The preferred range of operation is at 400-.600 mm. Hg with a -66 .veight'perc'ent acid extract. 4

. In La vs'ec'onjd Jjrno'dilfic'zation off vthis invention the f stripping foccurs with "the -aid of 'an y#inert `eas suchlas N2, CO2,'etc."or with a propylene-co'ntaining gas such as propylene itself or the propy- L Iene feed gas or theipropylene-containing-gases recovered from "the' ftilaterjscrubber via line 3| and 34. 'In the .employment of the'latter gases they are recycle-cyprus@ ftdfto theFslerator t; entering rthrough-line 1. `When`these inert'r propylene-:containing fgasesfare employed the stripping need' not vbe done under the vacuum-'required in theirfabsenoej-but jhigher pressursup to and including" atmosphericpressuie maybe employed. VAVV-lienthe invention vis -carriedo'utaccording to thisfsecondjmodication the vuse'lof propylene 'or la V*propylene-c'c'intaining -gas'is' preferred inasmuchasthis'has'atendency to minimise propylene {regeneration --fro'mlthe extract. When employing'these gases as stripping agents it is preferred to maintainpartialpressures-of isopropanol, isopropyl ether v"and V'u (ater in the range of"subatinosphericpressure. The'a'mount of strippingV gas' andfttalpress'uretare I'so regulated in order 'ythat these '-partialfpres'sureswill obtain. Ihe"sum V of the partial press'ures of isopropanol, isopropyl' eterand water therefore will vlie inthe` range of 200-750 Ihm.,@pre:ferably 40o-eco mm. Y

In furtherjdeparture Afrom the prior art practices, vthere is removed V(in the fo'rm` of isopropanol andis'opropylether) lfrom the generator by stripping only -a sniall uan'iount say 3-20'925, preferably iv-10%, of thefpropylene contained in the acid'extract entering '-th'fgeerator. "Iov vthis extent "thereforel the r-ac'ic'i extract is not diluted with Water befo're'-entering' jthe genea'tonand-fin the stripping erationfonly suficint 'steam'is added to thejgenerator vvia-lined toreplace that water requiredto 'hydrate the propylene son re- Amoved in the 'io'rm of alcohol and/ or ether. vaporsof theilattercontainingf some regenerated -propylene arefremoved from` the 1 generator `via line 8- for further processing as will'be described below.

vI-Iot acid extractor reduced saturation (he. reduced in saturation-by '5`l0%"due"to removal qor 'p that f amount ofpropyleneY in' the form 0f g1- cohol or ether) is 'ir-'einovedy as' bottoms from genuerator V(i via line 9;'coled`incooler 10j ledfby'pipe Il to pump l2," andreturn'ed via"lines f3 'and 3 'A tothe upper'sectin othe'absorber l-iorfurther Areaction with 'Y the feed gas. "Make-iup acid if needed'is added to theextract viaeline 14.

Overhead "vapors from theV generator," consisting of isopropyl alcohol of approximately 55-75 vweight percent strength, isopropyl ether, and propyleneenter a caustic scrubber I5 at a point near the ymid-section thereof. The vapors are countercurrently scrubbed with dilute aqueous caustic solution (2-10%) entering the top ofthe sate drum via line 22 and pumped by pump 23 through pipe 24 to storage (-not'shown). Un-

condensed gases containing propylene and somey alcohol and ether vapors are vented from the condensate drum by pipe 25. These vapors are introduced into the bottom of water scrubber 26 wherein they pass upwardly in countercurrent flow to descending water introduced through line 21. Only suii'icient water is fed to the scrubber to wash the major portion of any alcohol and ether vapors from the gas'. The recovered alcohol and ether in aqueous solution flow via line 28 to be pumped through pipe 30 by pump 29.

where they are mixed with the condensate in pipe 24 and sent via pipe 36 to storage. Overhead vapors consisting substantially of propylene pass through the steam ejector 32 fed by steam line 33 and are removed from the system Via linev I 34. These gases may he burned or recycled to the absorption zone according to existing economic dictates.

It is also a feature of this invention to strip isopropyl ether from the crude alcohol and return the ether to the absorption zone to repress ether formation therein, thus allowing a greater overall alcohol/ether production ratio. In this aspect of the invention crude alcohol is withdrawn via pipe 31 to distillation vessel 40. Ether is distilled overhead via line 38 while the etherfree alcohol is recovered as bottoms via line 39. Part of the ether is removed via line 4I and with the assistance of pump 42 is pumped via line 43 into the stream of acid extract on its way back to the absorber I.

The invention is illustrated by the following Working example:

Propylene is countercurrently absorbed in suliuricv acid in an absorber until an extract containing a propylene:sulfur1c acid ratio of V1.2 is

established, the extract containing about 60.0 weight per cent H2SO4. The extract is conducted to a stripping zone where it is subjected to flash vaporization at a pressure of 200 mm. absolute, such that 5-10% of the solution was vaporized. During'the vaporization the acid concentration of the extract in the still increased to about 63 weight percent, while the propylenezsulfuric acid ratio fell to about 0.950. The condensed distillate recovered from the vaporization contained approximately V75 weight percent isopropanol, 2-3% isopropyl ether and the balance water. YAYSmall amounts of propylene (about 5% of the total propylene evolved as alcohol ether and propylene) were also recovered.

The distillate was concentrated to a composition approaching that of the usual 91.3 volume percentv azeotrope in the manner Well known in the isopropanol rening art. The 63 weight perf vcentacid extract was 4"withdrawn from the bottom ofthe vaporizatinaoneandreturned to the top of the absorber where it absorbed additionalpropylene .to restore its saturation tothe mol ratio of about 1.2.' Water was added to the solution to `bring its acid concentration back to 60weight percent and thev cycle repeated.

. 1t. hasbeen further found from experiment that yildspi isoprpanol can b e obtained from 61.5 weight percent acid vextractlcy stripping atV about 200mm'. pressure which are practically equivalent .to those realized from"46.0 weight percent vacid at atmospheric pressure stripping, the latter diluy tion anddistillation representing that commonly 'used commercially' at 'the present time..

.Figure Zshows the composition of the distillate v`vslrk absolute I pressure. Vin 'the stripping zone for thedistillatioof a 61.5 weight percent H2SO4 extract'havingia incl saturation of 1.06. Figureshogws thecompositionof the-total overhead .from the stripping'z'one including propylene. 'l`hese guresshow that by suiciently reducing the'pressure on the stripping zone one obtains vyields of alcohol andiether from this extract 'which are comparable to those' obtained by stripping .a much more dilute extract of approximately the .fsame saturation (about 45 weight percent) at atmospheric pressure. The latter which typies present day commercial operationis summarized in the following table:

. A Table Iv Composition of distillate and yields of products basedA on "prop'ylene V'for 46.0%' acid, :l:k equalsA 1105,` distilled at atmosphericpressure.

" WeightV percent compostionlgofdistillate: Y I

1t has also been determined that acid extracts cf approximately 10 weight percent H2SO4 represent the upper limitlof acid strength of extracts to be subjected'vtovacuum stripping according t0 this inventions-.LI'huawhen a propylene:sul

.furic acid extract of 1. 06 saturation containing comprises absorbing a fluid' comprising propylr ene in sulfuric acid of 60-70 weight percent conmols of propylene per. mole of sulfuric acid from I I acid extract having asaturation lof 0.6 to 1.5

- the absorption zone, passing said extract without vdilution with Water to a strippingzone, removing -a hydration product distillate from the stripping zone comprising 3-20% of the propylene in the acidextract in said stripping zonerecovering accendo 7 'aci`dstrength from the'stripping zone, Adiluting the acid extract with Water vto restore the acid strength thereof "to "60-"7'0- 'weight percent and returning the'diluted' cxtractto the absorption zone. f

2. A procession: 'tlieproduction of isopropanol oy indirect hydrationof propylene which comprises absorbing a "duid comprising propylene in sulfuric Vacid i of '60.-70 vWeight percent n concentration inanjabscrptionzonefremovns an acid extract having Ya saturaticnofp-.eto n1.5 mois'cf propyleneperfniolejof sulfuric'"acid from the absorption zone, l'p'afssirrgsaid 'withdrawl 'extract without dilution/:With VWater'to a stripping zone, introducing an inert 'stripping gas intoy the stripping zone, removing a lnvtiration product distillate from. thestripping zoneifcomp'rising 3-20'% of the "propylene `inftlre acid Yattract; in said stripping none, recovering isoprop'anol from the distillate, Vremoving "an "acid "extractj of decreased saturation and increased acid strength from' the stripping zone; diluting thea'cid extract With Water "to restore 'the acid strengtlfi thereof to 60-70 weight percent'and returning the dilluted extract to the absorption zone.A

3. A process according' to claim '2 -inrvhich the acid extract is diluted with Water in the form of steam introduced V"to 'the generator withithe stripping gas. i K f 4. A process for the production of 'isopropanol by indirect hydration'oflpropylene which comprises absorbing a fluid comprising propylene in sulfuric acid of 'G0-,70"Wei`ght`p'ercent concentration in an absorption zonefreino'ving an' acid extract having a saturation of 0.6'to 1:5 moles of propylene per mole oisulfuric aciddroni the absorption-zone, passing. `said Withdrawniextract Withoutv dilution with Water to .a flashV stripping zone operated-at a...pressure below atmospheric pressure, removing ahydration product distillate from the stripping zlone'comprisnig 3-2`0% or" the propylene in' the 'acid extract in said stripping Zone, recovering 'isopropanol 'from the distillate, removing an'acid extractdf decreased saturation and increased -acid strength frorn the stripping vzone, diluting the acid extract with water to restore the acid strength thereof to '60J7f0 fivei'ghtipercent 'and returning the diluted extract to the'labsorption none.

f5. A processfaccording to claim 4 in which lthe acid 'extract is diluted Withvvater in theform of steam added tothe stripping zone.. I l

6. A'process'i'or the'productiori of isopropanol lay-indirect hydrationoi propylene which coinprises absorbing a iiuid'comprsing propyl'ene in sulfuric acid of 65-80 Weight' percent concentration in an 'absorption `Zone, removinglan acid extract havinga saturation of-0.9`to `1.`3 moles of propylene per mole of sulfuric acid irornthe absorption Zone, passing said Withdrawn extract without dilution with water to a ria-sh vstripping zone operated at a pressure below atmospheric pressure, removing a hydration product distillate iromthe stripping Zone comprising 5-l0% 'ofthe -propy-lene'in the acid extract in said stripping Zone,- "reco'vering isopropanol from the distillate,

-Aremoving ari-acid extract of decreased saturation I andincr'easedacid strength 'from'the 'stripping Jamie, diluting the acid extract 'with-water to 're- 'stor'e theacid Vstrength thereofto 65-68 Weight percentandfreturning thediluted extract to the absorption l zone.

'7. Aprocess according' to claim 4 in which the absolute.l

8 8. -A process for producing isopropanol by indirect hydration of propylene which comprises absorbing a fluid comprising propylene'in a sulfuric acid extract containing 60-'70 Yweight percent acid in ari-absorption zone, removing-an 'aci dext1act having` a saturation of 0.6 to 1.5 moles oi propylene per mole of sulfuric acid'froin the Vabsorption-zone,"passing said Withdrawn eX- tractwithout dilution with Water to -a' iiash strippingzone'operated at a pressure below atmospheric pressure, removing a hydration product distillate, `from-"the stripping y zone comprising 3f- 20% of the propylene vin the acid extract in said stripping `zone, recovering isopropanol from the distillate, removing an vacidextract ofde- "creased saturation and increased acid strength from-the strippingzone, diluting the racid extract with' Water to restorethe acid strength thereof to 60-70- Weight percent, and returning Vthe di- -luted extract to the absorption zone.

" 9. Aprocess for producing isopropanol 'by indirect hydration oi-proplylene which comprises absorbing a nuid comprising propylene in I-aV sulfur-ic acid-extract containing 65-68 Weight percent acid yinthe absorption zone, removing an acidextract having a saturation of 0.9 to 1.3 Amoles 'of propylene per mole of sulfuric acid from the absorption zone, passing said Withdrawn extractfwithout dilution ivith Water-toY a `iiash jstrippingzcne operatedat a pressure below atmospheric pressure, removing a hydrationlproduct- Ydistillate from the strippingzone l comprising 5-10-70 of 'the propylene in `the -acid extract in said stripping Zone, recovering Aisopropanol from 'the' distillate, removing an acid extract of decreased VSaturatien 'and increased acid strength from' the 'stripping zone, diluting thc-acid extract with Water to restore the acid strength thereof to -GBK-GBWei-ght percent, and returning the diluted extract-"to theabsorptionzone.

V10.- Aprocess according tecla/im' 9 in which 'the pressure inthestripping zone is '20G-G00 Inim.

absolute. A

" .11. A process for producing isopropanol by indirect hydration o 'propylene which lcomprises absorbing a iluid comprising propylene in a'sul- 'furie-acid extract containing 60-70 Weight percent acid in an absorption zone, removing an acid extract containing 0.6 to 1.5 moles of propylerated. at a pressure below atmospheric pressure, vremoving ka 'hydration product-distillate 'from the s'tripping zone comprising 3-'20% of the'propylene 1n the acid extractin -saidstripping zone, v'adding sufcient water inthe form of Asteam tothe strippin-gache lto compensate vonly for thatvvater coniromthe `stripping zone, recovering isopropancl from-the distillate, removing Aan-acid extract-of decreased saturation but still containing 60-70 Vabsorption zone.`

` 12v;- A process for producing isopropanol byiny direct hydration of propylene which comprises absorbinga iluidcomprising propylene in-a sulfuricacid extract'containing 65-68 Weightpep centacid in-an'absorption zone, removing anacid extract containing 0.9 to 1.3 moles of -propylene Vper mole Vof sulfuric'acid from the absorption none, passing said withdrawn vextract without di- 'Y lution-.With Water to a flash strippingizone--operated at a pressure below 4atmospheric pressure,

removing a hydration product distillate from the stripping zone comprising 5-10% of the propylene in the acid extract in said stripping zone, adding sucient Water in the form of steam to the stripping zone to compensate only for that Water consumed in forming the hydration product removed frcm the stripping zone, recovering isopropanol from the distillate, removing an acid extract of decreased saturation and still containing 65-68 Weight percent acid from thestripping zone, and returning the withdrawn acid extract to the absorption zone.

13. A process according to claim 12 in which the pressure in the stripping zone is 200-600 mm. absolute.

14. A process according to claim 12 in which the absorption of propylene by the acid extract is carried out countercurrently.

15. A process according to claim 12 in which isopropyl ether is also recovered from the hydra-V Vtion product and at least a portion of the re'- covered ether is recycled to the absorption zone.

ERWIN H. AMICK, J R.

REFERENCES CITED The following references are of record in the le of this patent: 

1. A PROCESS FOR THE PRODUCTION OF ISOPROPANOL BY INDIRECT HYDRATION OF PROPYLENE WHICH COMPRISES ABSORBING A FLUID COMPRISING PROPYLENE IN SULFURIC ACID OF 60-70 WEIGHT PERCENT CONCENTRATION IN AN ABSORPTION ZONE, REMOVING AN ACID EXTRACT HAVING A SATURATION OF 0.6 TO 1.5 MOLS OF PROPYLENE PER MOLE OF SULFURIC ACID FROM THE ABSORPTION ZONE, PASSING SAID EXTRACT WITHOUT DILUTION WITH WATER TO A STRIPPING ZONE, REMOVING A HYDRATION PRODUCT DISTILLATE FROM THE STRIPPING ZONE COMPRISING 3-20% OF THE PROPYLENE IN THE ACID EXTRACT IN SAID STRIPPING ZONE, RECOVERING ISOPROPANOL FROM THE DISTILLATE, REMOVING AN ACID EXTRACT OF DECREASED SATURATION ZONE, DILUTING THE ACID STRENGTH FROM THE STRIPPING ZONE, DILUTING THE ACID EXTRACT WITH WATER TO RESTORE THE ACID STRENGTH THEREOF TO 60-70 WEIGHT PERCENT AND RETURNING THE DILUTED EXTRACT TO THE ABSORPTION ZONE. 